1. Field of the Invention
The present invention relates to a lighting apparatus in which light source(s) such as LED(s) and a light-focusing lens are combined.
2. Related Art Statement
Conventionally, many of lighting apparatuses used for reading and writing CDs, DVDs or used as a backlight system in various optical applications include a support, a light source such as an LED, lamp or the like attached to the support, a lens attached to or formed integrally with the support to face the light source, and are configured to illuminate brightly a predetermined object or scope so as to have a predetermined property to focus light emitted from the LED and so on.
FIG. 9 illustrates a first conventional lighting apparatus. The lighting apparatus has a frame-like support 40, a chip-shaped LED 41 disposed in the support, and a lens 42 supported on the support 40 so as to face the LED. The lens 42 comprises a semi-spherical transparent member, and has a regular convex lens surface 42a. An emission surface (usually, an upper surface) of the LED 41 is disposed in the vicinity of a focal position of the lens 42 or in a position remote from the focal position appropriately. The LED 41 is mounted on a substrate 43 attached to the support 40 and supplied with an electrical power for emission through bonding wires 44. Meanwhile, the LED 41 and the bonding wires 44 are encapsulated by a sealing member 45, which comprises a transparent resin.
However, in the first conventional lighting apparatus, because the lens has a semi-spherical shape, the entire thickness of the lighting apparatus increases. Therefore, a lens having a Fresnel lens surface possible to thin a thickness is often used in place of the lens 42. Here, the Fresnel lens surface means a surface which comprises a convex lens part at the center thereof and a series of coaxial fine prisms each having a right triangle-like shape in section formed coaxially to a central axis of the convex lens. In such a lens, when the ring-like prismatic portions are equal in height in order to minimize the entire thickness, an inclined surface of each prismatic portion rises up as going to a peripheral part of the lens, an apex angle of each prismatic portion becomes sharp, a radial space between the adjacent prismatic portions also becomes narrow rapidly. Accordingly, when a transparent member made of a usual resin material is formed by cutting directly or a forming die, the manufacturing of the peripheral part of the lens is very difficult.
When the LED is located on an optical axis of the lens, a beam of light enters bottom surfaces of the prismatic portions obliquely at the peripheral part of the lens, only a portion (lower portions) of the inclined surfaces of the prismatic portions is usable, hence the usability is lower. Under such circumstances, it is difficult to manufacture a lens including a Fresnel lens surface having a large aperture prefer to collect light, in which a ratio of an outer diameter to a focal distance in the lens is larger and the inclined surface of each prismatic portion at the peripheral part is sharp, the performance also has no advantage over the usual lens.
On the other hand, if the LED 41 is used keeping a natural luminescent color, the structure shown in FIG. 9 is sufficient for the lighting apparatus, while if a light source color different from the luminescent color of the LED 41 is used, for example, when a white light source is desired to obtain by use of a blue color-emission LED, by using a material containing a YAG fluorescent substance into the transparent sealing member 45 for sealing the LED 41, the white color emission can be acquired as a whole by exciting the fluorescent substance according to the emission of the blue-color LED 41 to generate light having a long wave length, and by a color mixture of the LED emission and the sealing member emission.
In this case, when the LED does not emit the light and a person watches the sealing member 45 through the transparent lens 42 from the outside, the person can see the sealing member 45 taken on yellow tinge by outside light, because the fluorescent substance is included in the sealing member 45. This results in damage of an exterior appearance of the lighting apparatus.
To improve the defect, in a second conventional lighting apparatus, a light-scattering plate 46 is disposed in a front of the LED 41 in place of the lens 42, as shown in FIG. 10. The light-scattering plate 46 presents white color scattering outside light, has an effect that the back yellow sealing member 45 does not see almost. However, because the emitted light from the LED 41 is also scattered in the structure, even if a light-focusing lens is used, it is not possible to collect light, or the lighting apparatus becomes incomplete.